Technical Field
The present invention relates to a communication device that is connected to a home network, which is a network in a home, to provide services to each other. Particularly, the present invention relates to a communication device that achieves a reduction in power consumption due to a reduction in standby power, and an automatic discovery and an automatic cooperation of communication devices present in the network.
Background Art
In recent years, as the information-oriented society has been developed, networking at home has been quickly spreading. Since a communication device connected to the network at home is used not by an engineer but by a general home user, setup operation of the communication device must be as easy as possible.
Additionally, by the communication devices connected through the network cooperating with each other, in other words, by the communication device operating while controlling the other communication devices, enhancement of the convenience of services provided by the communication devices is anticipated.
In general, when controlling other communication devices present on the network, it requires acquiring IP address information of a communication device to be controlled and setting for it, as well as acquiring information, including the type of the communication device to be controlled and the service provided by the communication device and setting for it. As a method for acquiring the IP address or the service information of the communication device to be controlled, a service discovery protocol such as UPnP (Universal Plug and Play) is known. In order to automatically discover the communication device to be controlled and to acquire the IP address or the service information using such a service discovery protocol, however, there is a problem that a power supply of the communication device to be controlled must be turned on.
Namely, in order to keep the communication device connected to the network in a state where it can automatically be discovered, the power supply of the communication device must be normally turned on.
However, in recent years, with the rise of the consciousness to energy saving, a reduction in standby power of each communication device has been desired, so that a usage mode where the power supply is always turned on has been regarded as problematic.
In response to this problem, there is known a power supply controlling method which provides two energization states in the communication device, wherein (1) when a main-power supply is in an off-state, a sub-power supply energizes only a network device which performs the processing regarding the network, and (2) when a power supply starting packet is received from the network, the main-power supply of the communication device is turned to an on-state to service all the communication devices (for example, see Patent Reference 1).
While, for example, each communication device transmits a discovery packet in order to search for the communication device to be controlled, this method makes it possible, by transmitting the power supply starting packet before transmitting the discovery packet, to search for the communication device even when the main-power supply of the communication device is in an off-state.
Meanwhile, in another parallel computer system, in order to enable a controlling device to manage the status of the respective operational units and to control the power supply thereof, there is known a method wherein an auxiliary device connected to each operational unit is energized by the sub-power supply when each operational unit is in an off-state, and wherein the auxiliary device processes a response to a status inquiry from the controlling device and a correspondence to a request of controlling the power supply (for example, see Patent Reference 2).
In this method, when the auxiliary device receives the power supply starting packet from the controlling device, the power supply of the operational unit is turned to an on-state, so that the operational unit is turned to a fully operable state.
By performing such control, the parallel computer system makes it possible to achieve a reduction in power consumption and a reduction in rush power upon turning on the power.    [Patent Reference 1: Japanese Unexamined Patent Publication No. 2003-244157    [Patent Reference 2: Japanese Unexamined Patent Publication No 1997-97241
However, the conventional power supply controlling method described in Patent Reference 1 simply enables, when a new communication device is connected to the network (namely, when the communication device with which the power supply is already turned on has acquired a list of the communication devices to be controlled connected to the network), the power supplies of all the communication devices connected to the network to be turned on for acquiring communication device information. Hence, there is a problem that, with the protocol such as UPnP (Universal Plug and Play) where the inquiry of the communication device to be controlled is transmitted irregularly by multicast over the network, it can not expect the power-saving effect.
Additionally, in the protocol such as UPnP, each communication device is required to notify that the communication device itself is in a state of being able to provide the service by transmitting an alive packet by multicast for every certain period. Since the periodical transmission of the alive packet can not be solved by the conventional power supply controlling method, it is necessary that the power supply is always turned on in order to transmit the alive packet.
Moreover, in the prior art described in Patent Reference 2, as a trigger to restore the operational unit from a power-saving operation state to a normal state, there is transmitted a request packet (power supply starting packet) which is for the controlling unit on the controlling side to restore a specific operational unit to be controlled to the normal state. As a result, in order to transmit the request packet to properly restore the specific operational unit to be controlled to the normal state, there is a problem that the controlling device on the controlling side must realize whether the operational unit to be controlled is in the power-saving operation state or in the normal state.
In view of the foregoing problems, it is an object of the present invention to provide a communication device which enables to discover a desired communication device using the service discovery protocol such as UPnP while the main-power supply of the communication device to be controlled on the network is in an off-state, without the communication device on the controlling side being conscious of the status of the communication device to be controlled.
In addition to that, it is a second object of the present invention to provide a communication device which enables to control the discovered communication device to be controlled, without the communication device on the controlling side being conscious of the status of the communication device to be controlled.